The present invention relates to lighting and more particularly to a lamp assembly for use in connection with inductively powered lighting.
Although not widely available, inductively coupled lighting systems are known. A conventional inductively coupled lighting system generally includes a primary circuit having a primary coil (or xe2x80x9cprimaryxe2x80x9d) that is driven by a power supply and a secondary circuit having a secondary coil (or xe2x80x9csecondaryxe2x80x9d) that inductively receives power from the primary. Inductive couplings provide a number of advantages over conventional direct electrical connections. First, inductively coupled lamps are typically safer and easier to connect and disconnect than hardwired lamps. With direct electrical connections, it is generally necessary to manipulate electrical connectors when installing and removing the lamp assembly. This typically requires some effort and creates a risk of electrical shock. Often, the electrical connectors are at least partially exposed, thereby increasing the risk of electrical shock. Inductively coupled lamps, on the other hand, do not require the manipulation of any electrical connectors. Instead, the secondary of the lamp assembly simply needs to be placed adjacent to the primary to permit the supply of power to the lamp assembly. Second, the elimination of electrical connectors also increases the reliability of the system by eliminating the problems associated with conventional electrical connectors. For example, conventional electrical connectors are subject to corrosion and to wear. These problems are particularly acute in an outdoor setting where environmental conditions may subject the electrical connectors to moisture. With repeated use, mechanical connectors are also subject to wear and eventual failure. Third, inductively coupled lamps inherently provide a lower risk of an electrical hazard at the lamp assembly. As noted above, the lamp assembly is electrically separated from the power source. All power must be inductively passed from the power source to the lamp assembly. Because there is an intrinsic limit on the amount of power that can be inductively passed to the lamp assembly, the amount of power at the lamp assembly is limited and the risk of electrical hazards is reduced.
Although conventional inductively coupled lamps provide a number of important advantages over directly connected lamps, they do suffer significant drawbacks. An inductive coupling is inherently less efficient than a direct electrical connector. This is partly due to the power required to create and sustain the electromagnetic field. The primary inefficiencies in a conventional inductive coupling result from a poorly tuned circuit. These inefficiencies are manifest in increased heat gain and in noise created by vibration in the primary and secondary. The efficiency issues are exaggerated with higher power lighting applications. In addition, existing lamp circuits require precise alignment of the primary and secondary to provide any reasonable level of efficiency. This requires more precise tolerances and limits the configuration and layout of the lamp assembly and the overall lamp.
One of the largest reliability issues facing the lamp industry is caused by the penetration of the lamp sleeve by wires or other electrical conductors. Typically, the wires pass into the interior of the lamp through a glass stem. Because glass does not readily adhere to and seal around the wires, there is a material risk of lamp leakage at the point the wires penetrate the lamp. Although efforts have been made to optimize the seal, this remains a significant reliability concern.
With conventional inductively powered lamps, there are also reliability issues associated with exposure of the lamp circuit components to the environment, for example, water and moisture from the environment can damage circuit components. To address this concern, at least one inductively powered lighting system encloses the entire lamp assembly within a sealed enclosure. U.S. Pat. No. 5,264,997 to Hutchisson et al discloses a lamp that is mounted to a printed wiring board that is spaced from the secondary on a plurality of posts. The printed wiring board includes various electrical component required for operation of the inductive coupling. Separate shell and lens components are sealed together to form a leaktight enclosure around the lamp, the printed wiring board and the secondary. The shell is specially shaped to receive the secondary and to be interfitted with a socket containing the primary. Although the sealed enclosure provides improved protection from environmental conditions, it is relatively bulky and only provides light transmission in the direction of the lens.
As can be seen, there remains a need for an inductively coupled lamp assembly that is efficient, provides improved reliability in a variety of conditions and is easily adapted to many different lamp configurations.
The aforementioned problems are overcome by the present invention wherein a lamp assembly is provided with a lamp, an inductive secondary for powering the lamp and a capacitor. The capacitor is connected in series with the lamp and the secondary, and is selected to have a reactance at the operating frequency that is approximately equal to or slightly less than the combined impedance of the lamp and the secondary at operating temperature. As a result, the lamp circuit operates at or near resonance. With electric-discharge lamps, the series capacitor also functions to limit the flow of current in the secondary circuit, precluding an uncontrolled increase in current that would otherwise occur with an electric-discharge lamp.
In another aspect, the present invention provides an inductively powered lamp assembly in which the entire lamp assembly circuit is sealed within a transparent sleeve. Preferably, the entire lamp assembly circuit, including secondary and any associated capacitor, is sealed within the sleeve of the lamp. In an alternative embodiment, the secondary and lamp, as well as any capacitor and starter device, are contained within a second closed plastic, Teflon, glass or quartz sleeve with no wires or other elements penetrating the sleeve. The void defined between the second sleeve and the lamp sleeve is preferably evacuated or filled with a functional gas to provide the desire level of heat conduction or insulation.
In a further aspect, the present invention provides a remotely actuated switch to provide preheat of electric-discharge lamp. The switch is provided to short the electrodes across the secondary for a specific period of time at lamp start-up. In addition this circuit may have a series resistor to help limit preheat current. In one embodiment, the switch is an electromagnetic switch that is preferably actuated by a magnetic field generated by a corresponding coil in a lamp control circuit.
The present invention provides a simple and inexpensive lamp assembly for use with inductively powered lighting. Because the lamp assembly operates at or near resonance, it has a high power factor and is highly efficient. This reduces power loss through heat build up and also provides for quiet operation of the inductive couplingxe2x80x94even in relatively high power applications. The efficiency of the secondary circuit demands less precise alignment between the primary and secondary, thereby permitting a greater degree of latitude in the layout and configuration of the lamp and the lamp assembly. The sealed sleeve provides the lamp circuit with improved protection from the environment without limiting the transmission of light from the lamp. Although with some light sources, the spectrums emitted may see losses based on the specific transmissive properties of the materials used in the sleeves, for example, some materials are not highly transmissive to UV light. The present invention allows functional gases to be entrapped within the sealed sleeve to increase or reduce the degree to which the lamp is isolated from the environment. Further, by enclosing the entire lamp circuit within the lamp sleeve, the need for wires or electrical leads that penetrate the sleeve can be eliminated. This greatly improves the reliability of the lamp while dramatically reducing manufacturing losses. Also, the electromagnetic switch of the present invention provides an inexpensive and reliable alternative to conventional starter circuits.
These and other objects, advantages, and features of the invention will be readily understood and appreciated by reference to the detailed description of the invention and the drawings.